This invention relates to offset printing, and in particular to a safety interlock system for electrically deenergizing the drive motor of an offset printing press having a plate cylinder-containing printer head and a dampening and inking roller-containing carriage movable to and from the printer head. Such deenergization is initiated upon predetermined press operating conditions which jeopardize operator safety.
During operation of an offset printing press, it is necessary from a safety standpoint to limit operator access to the rotating plate and blanket cylinders. Numerous covers which activate associated "kill" switches when opened can be used to deenergize the press drive motor and thus preclude operator access to the press cylinders during a running condition. However, such covers are not readily adaptable as the sole solution to operator safety when a press of the earlier noted movable-carriage type is considered. When a dampening and inking roller-containing carriage is moved away from the printer head containing the plate cylinder with which the carriage-contained rollers are engageable, means must be provided to deenergize the press motor to preclude operator access to the rotating plate cylinder when it is exposed by such withdrawal of the carriage. However, such means for precluding access to the rotating plate cylinder must permit rotation of the carriage dampening and inking rollers by the press motor for wash-up purposes when the carriage is withdrawn from the printer head and the plate cylinder is in a nonrotating condition due to its disengagement from the blanket cylinder.